1. Field of the Invention
The present invention relates generally to x-ray systems, devices, and related components. More particularly, embodiments of the invention relate to brazed x-ray target assemblies that include an oxide dispersion strengthened (ODS) alloy substrate and a carbon-based heat sink and methods for manufacturing such x-ray target assemblies and related devices.
2. Related Technology
The X-ray tube has become essential in medical diagnostic imaging, medical therapy, and various medical testing and material analysis industries. An x-ray tube typically includes a cathode assembly and an anode assembly disposed within an evacuated enclosure. The cathode assembly includes an electron source and the anode assembly includes a target surface that is oriented to receive electrons emitted by the electron source. During operation of the x-ray tube, an electric current is applied to the electron source, which causes electrons to be produced by thermionic emission. The electrons are then accelerated toward the target surface of the anode assembly by applying a high-voltage potential between the cathode assembly and the anode assembly. When the electrons strike the anode assembly target surface, the kinetic energy of the electrons causes the production of x-rays. Some of the x-rays so produced ultimately exit the x-ray tube through a window in the x-ray tube, and interact with a material sample, patient, or other object.
Stationary anode x-ray tubes employ a stationary anode assembly that maintains the anode target surface stationary with respect to the stream of electrons produced by the cathode assembly electron source. In contrast, rotary anode x-ray tubes employ a rotary anode assembly that rotates portions of the anode's target surface into and out of the stream of electrons produced by the cathode assembly electron source. The target surfaces of both stationary and rotary anode x-ray tubes are generally angled, or otherwise oriented, so as to maximize the amount of x-rays produced at the target surface that can exit the x-ray tube via a window in the x-ray tube.
In an X-ray tube device with a rotatable anode, the target has previously consisted of a disk made of a refractory metal such as tungsten, and the X-rays are generated by making the electron beam collide with this target, while the target is being rotated at high speed. Rotation of the target is achieved by driving the rotor provided on a support shaft extending from the target. Such an arrangement is typical of rotating X-ray tubes and has remained relatively unchanged in concept of operation since its induction.
The operating conditions for X-ray tubes have changed considerably in the recent decades. Due to continuous demands from radiologists for higher power from X-ray tubes, more and more tubes are using composite rotating anodes with tungsten-rhenium as a focal spot layer, molybdenum alloy as a substrate, and brazed graphite as a heat sink.
Increasing the power levels of the x-ray tube is typically accompanied by an increase in the operating temperatures of the anode, which, if high enough, may result in deformation of the molybdenum alloy substrate. Deformation in the substrate can cause large stresses in the metallurgical bond between the alloy substrate and the graphite heat sink. Should the stress exceed a threshold value, a complete debond of the graphite heat sink can result. The magnitude of this stress imposes a limit on the maximum size, rotational speed and highest allowable temperature of the alloy substrate.
To overcome the problem with deformation of molybdenum alloy substrates at elevated temperatures, other Mo-bearing alloys have been considered by x-ray target manufacturers. Oxide dispersion strengthened (ODS) Mo alloys currently show promising performance for reducing deformation of the substrate at high temperatures.